Posted November 30, 201410 yr Hi guys, I'd like to share my version of a C-model of the 42008 Service Truck. I was inspired by the great TC5 contest, even though this doesn't qualify to it due to the part count. Nonetheless, only parts from the set 42008 are needed to build this model. This is actually my first actual MOC, I've only done mods and small concepts before. Still, this is already the 3rd tail lift implementation I post here :-) This time I'm using the small pneumatic cylinders, now attached to a small green delivery truck. Here are some pictures: It has the following features: - HOG steering - tail lift with controls for elevation and tilting it - manual pump behind the seats - openable doors - openable container space roof - openable upper part of the rear door Now some words about the tail lift. Here's the LXF model of it, and a picture: The cylinders are replaced in LXF by yellow 5M beams. The right hand side cylinder provides the lifting mechanism, and the left hand side cylinder tilts the lift (basically only closes or opens the lift when in the elevated position). Now, it's probably no surprise that the lift is very weak. It is raised only by the right hand cylinder, and the mini pneumatic cylinder isn't that powerful. Also the travel of the lift is much greater than the 2M travel of the cylinder itself, so it has to overcome quite a bit of mechanical disadvantage. Tilting the mechanism works fairly well, as there's not much force needed for closing or opening the back door; when using the door as a lift all the weight is carried by the completely retracted cylinder and not air pressure. (Which, of course is not completely realistic, but must be like this at this scale.) Despite being weak, I'm quite happy with the lift mechanism. It follows real design of these lifts quite closely. In optimal circumstances it can lift small loads, but typically it's not that useful. The reason is a bit unexpected: I discovered that a major force resisting lift travel was actually the pneumatic hoses that must also bend and move when the lift rises or lowers. There's not only the air pressure resisting bending of the hose but also friction when they rub against each other and the walls of the truck. Therefore I added a couple of rollers for each hose and also encapsulated them in the pin joiners that have much less friction when touching other parts. I didn't include a compressor, as I felt that manual pump would give slightly more pressure to the cylinders, and would be more appropiate for a model of this size. Also I'm not too fond of the vibrations the compressor creates. To operate the pump, you need to open the right side door and use the lever behind the seat (up/down). I haven't yet created an LDD version of this, but will get to that soon. After doing that, I'm looking into possibilities of using mini-LAs for the tail lift, as the model also has a pair of those. They are longer and take more space, but I'm sure they would work better. I don't know whether that means motorizing it or not, but we'll see. Thanks for reading, I hope you enjoyed this!
November 30, 201410 yr That door mechasnism is just perfect! It looks and functions just like the real thing. Lovely hood too
November 30, 201410 yr Author Thanks for the nice comments. I only wished there were more green panels or liftarms in the set, would've done the truck a bit longer. But maybe this is a compact city truck... Cool mechanism! Do you plan to create video to show us it in motion? Ah yes... Here's a quick video of it: https://flic.kr/p/qfyznB (Sorry for the bad image quality, I don't really have the necessary gear and environment for decent videos at the moment.) As you can see, it struggles a bit to lift the platform. It's actually worse at the moment when going down. It's quite sensitive how the pneumatic hoses are positioned so that they don't put extra stress to the mechanism. Probably pressure in the other circuit affects this as well. Any ideas about how to get around that would be appreciated. One modification could of course be to use both cylinders for lifting and having the tilting (opening/closing) as a manual function.
November 30, 201410 yr It's a very cute truck The lifting mechanism is way cool. Years ago (like in last century) I tried to make such a lifting mechanism and failed spectacular, so I'm really impressed that you were able to fit it in such a small model. If you can somehow get the tubes to form a (large part of a) circle it is easier to move them. Moving them will then result in a change of diameter of the circle which usually doesn't require that much force.
December 1, 201410 yr Great little delivery truck and only from the 42008 no less. I might steal your tail lift mechanism for a truck I had in mind :)
December 2, 201410 yr Can someone please make instructions or at least a step by step photo/image with the pneumatics? I would love to recreate that with my 42008.
December 2, 201410 yr Author If you can somehow get the tubes to form a (large part of a) circle it is easier to move them. Moving them will then result in a change of diameter of the circle which usually doesn't require that much force. Yes, I think that's what needed. Unfortunately I'm constrained by the length of the tubes, especially the shorter pair. Maybe moving the switches higher could help (so the tubes don't need to bend so much back down). Hmm.. Great little delivery truck and only from the 42008 no less. I might steal your tail lift mechanism for a truck I had in mind :) Please do, there's way too few tail lifts in Technic mocs :-) I'd really like to see this in use. Can someone please make instructions or at least a step by step photo/image with the pneumatics? I would love to recreate that with my 42008. I'm going to make a Lego Digital Designer model out of this in the near future, but I don't have the skills to do actual instructions out of that. I think it's possible to modularize the model to a few segments so it can be built easier even without too long instructions. Meanwhile, I've been thinking about a variation with mini-LAs. Those are a bit too big for this model (3 x 1 x 7-10 versus 1 x 1 x 5-7 ), but I think I can squeeze them in. As the mLAs are longer, they need to be mounted deeper in the chassis, about where the rear wheels are located. Now that's a problem because there's only about 7M wide room for the two mLAs side by side. Also, because the mLAs must be mounted below the support beam (unlike in the pneumatic version), the beam cannot be immediately above them, but must be bent. Anyway, I came up with this: The mechanism will not use the whole range of mLAs, but that's probably not an issue. We'll see how this will work... Stay tuned!
December 3, 201410 yr Haha, since I was considering a motorized truck I was looking into doing it with mLA's too! Looks like you're saving me some work :)
December 10, 201410 yr Author I've been trying to get a mLA version out for this, but it seems I can't find a way that's not an ugly hack. The mLAs really are too long for this, and consequently, they require too sharp or shallow angles, which in turn don't work well when we have only 1 stud lever for the actuators. There's always something blocking movement. With small pneumatic cylinders, it was much easier as they could be placed on the side where not obstructing anything. I'll probably revisit the topic of tail lifts one day and construct a larger scale tail lift with mLAs. Even then their width will probably cause problems... Now, about the pneumatic version, I've made an LXF file out of it. It doesn't contain pneumatic tubes, and all the pneumatic components (cylinders, pump, and switches) are replaced by yellow parts. (The longer tubes from 42008 go the left hand side cylinder and shorter to the right hand side cylinder.) Also you might need to add a connector or two for holding the tubes. The total part count is about 600. I've made groups for the cabin, cargo space and tail lift in the LXF and they can be built pretty much independently. There's still long way for actual building instructions, which I don't have the skills to do.
January 4, 201510 yr Author Here's a modified version of the truck. I dedicated both pneumatic cylinders for the lift, and made a mechanical link for tilting the platform. It's not as neat as having both working pneumatically, but works better. As before, I only used parts from 42008 Tow Truck, but I have to say that I used two pneumatic T-pieces, while the original model uses only one. But as far as I know there's another T-piece as a spare in the set. The mechanical linkage works by turning the tan 20T bewel gear (located where the other pneumatic switch used to be), and it's geared down 5:3. There's a friction pin resisting movement so the tail door doesn't come down by itself. Here's a video (as you can see the lifting mechanism works decently) and also an updated LXF file (without pneumatic parts).
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